The present invention relates to an antenna, and more specifically to an dual-frequency broadband antenna.
A generic half-wavelength (xc2xdxcex) antenna is a so-called dipole antenna as indicated in FIG. 1, in which the distance between a positive and a negative pole of the antenna is theoretically arranged as shorter as possible to thereby obtain a better radiating and receiving effect.
In a conventional copper-duct dipole antenna structure (40) shown in FIG. 2, a coaxial cable (41) is penetratingly laid in a hollow copper duct (42) of xc2xc wavelength (xcex) long approximately, in which a conductive woven layer (411) of the coaxial cable (41) is connected to the hollow copper duct (42) to form a negative pole (xe2x88x92) while a bare core (410) in xc2xcxcex long approximately would serve for a positive pole (+). The effective bandwidth of such a conventional dipole antenna (40) is about 5.0xcx9c10.0% of a frequency band (that is, ratio of bandwidth to center frequency), 100xcx9c240 MHz for the frequency band of 2.4xcx9c2.5 GHz, for example. Unfortunately, however, the structure of this conventional dipole antenna (40) can be applied for a single-frequency band antenna only, not yet available for a dual-frequency band antenna.
To improve the structure of the mentioned dipole antenna to fit for a dual-frequency band antenna and widen the bandwidth thereof would provide an alternative for more effective radio communication. In this consideration, the inventor has endeavored to provide a novel dual-frequency broadband antenna in a proper length for high-performance signal radiation and reception.
The primary objective of this invention is to provide a dipole antenna set for signal radiation and reception in a low-frequency band, which is supposed to bring about the resonance vibration in a high-frequency band by adjusting the interval between a positive and a negative pole of the antenna to xc2xcxcex of the high frequency band approximately.
Another objective of this invention is to provide a structure of dual-frequency broadband antenna that can broaden the bandwidth of resonance vibration to about 25% by means of an inductive shield covered on the dipole antenna set.
Yet another objective of this invention is to provide a structure of dual-frequency broadband antenna, in which the interval between a positive and a negative pole of the antenna is adjusted to xc2xcxcex of the high frequency band such that the increment of the antenna under the function of dual-frequency band is limited shorter than xc2xcxcex of the high frequency band to present a decent appearance thereof.
In order to achieve the mentioned objectives, the structure of dual-frequency broadband antenna of this invention mainly comprises a dipole antenna set and an inductive shield, in which a positive and a negative pole are substantially two cup-like poles spaced out from a distance apart equal to xc2xcxcex of the high frequency band approximately; the inductive shield is a tube made of an insulating material, having a open end. The dipole antenna set is assembled in a cavity of the inductive shield without contacting the inner rim of the latter.
For more detailed information regarding advantages or features of this invention, at least an example of preferred embodiment will be fully described below with reference to the annexed drawings.